1. Field of the Invention
The present invention relates to an imaging apparatus, and in particular to an imaging apparatus which detects the focusing position of a photographing lens based on image signals obtained from an imaging element.
2. Description of the Related Art
In general, a digital camera is equipped with an auto focus (AF) system for automatically focusing a photographing lens. As the AF system of a digital camera, contrast AF for performing focusing with the use of output of an imaging element and outside light AF for measuring a distance with the use of an optical system different from a photographing lens are known.
In the contrast AF, a focus evaluation value indicating the sharpness of a subject image is calculated based on a high-frequency component in an image signal obtained from an imaging element, and a focus lens is moved to the position at which this focus evaluation value peaks.
Meanwhile, in the outside light AF, an infrared ray or an ultrasonic wave is emitted to a subject, the distance to the subject is calculated by applying the so-called principle of triangulation to a reflected wave from the subject, and a focus lens is moved to a focusing position corresponding to the obtained distance.
When the contrast AF and the outside light AF are compared with each other, the contrast AF excels in precision but has a problem that focusing takes time, and the outside light AF can quickly measure a distance but has a problem of being inferior in precision.
Accordingly, Japanese Patent Application Laid-Open No. 10-229516 proposes a digital camera which performs high-speed and high-precision AF by using both of the outside light AF and the contrast AF to switch them according to situations. For example, the high-speed and high-precision focusing according to situations is performed by usually performing focusing with the use of the high-speed outside light AF and performing focusing with the use of the contrast AF in the case of performing macro photographing. Furthermore, since the focusing precision of the outside light AF is degraded in a low or high temperature, the contrast AF is performed after the outside light AF in a low or high temperature, to perform the high-speed and high-precision focusing according to situations.
Furthermore, Japanese Patent Application Laid-Open No. 2003-75717 proposes a camera which extracts the face of a person from an image obtained from an imaging element and determines the distance to the subject based on the size of the face to perform focusing.
However, in the case of the camera with a system using both of the outside light AF and the contrast AF as that of Japanese Patent Application Laid-Open No. 10-229516, it is required to incorporate a distance measurement device for the outside light AF into the camera body, which is an disadvantage of increasing the cost.
Furthermore, there is also a problem that a photographer's intention of photographing is not exactly reflected because how the outside light AF and the contrast AF are used depends on the camera. That is, though a photographer wants to give priority to quickness over focusing precision when a good photo opportunity pops up and to focusing precision over quickness when he desires to carefully create a work, the camera of Japanese Patent Application Laid-Open No. 10-229516 cannot exactly respond to such a request by the photographer.
In the case of the camera which determines the distance to a subject based on the size of the face of a photographed person to perform focusing as that of Japanese Patent Application Laid-Open No. 2003-75717, it excels in quickness but has a disadvantage of being inferior in focusing precision.